The strtoupper() function in PHP is used to convert all alphabetic characters in a string to uppercase.

📌 Syntax:

strtoupper(string $string): string

Examples:

1. Basic usage

$text = "hello world";
$uppercaseText = strtoupper($text);
echo $uppercaseText;  // Output: HELLO WORLD

2. With mixed case

$text = "Php Is Awesome!";
echo strtoupper($text);  // Output: PHP IS AWESOME!

3. User input scenario

$name = "john doe";
echo "Hello, " . strtoupper($name);  // Output: Hello, JOHN DOE

Notes:

• It only affects alphabetic characters (a–z, A–Z).
• It does not affect numbers or special characters.
• It works with ASCII characters; for multibyte (UTF-8) strings, use mb_strtoupper() instead.

🔁 Example with form input

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $input = $_POST["username"];
    echo "Username in uppercase: " . strtoupper($input);
}